Location: Chicago (Over two miles from Wrigley Field. Fuck the Cubs. Fuck them in their smarmy goat-hole.)

Posts: 26,317

Total Cats: 1,915

Quote:

Originally Posted by JasonC SBB

Pressure cookers will hold more active material than the average pipe.

Yes, and that's where my knowledge of the physics of combustion really starts to become inadequate- how to judge the relative merits of a large volume of material in a vessel with a low bursting strength vs. a small volume of material in a vessel with a high strength.

Consider the most extreme possible examples. You could pour five pounds of powder out onto a wooden table, and then throw a lit match at it. The powder would vary rapidly deflagrate, producing a large amount of heat and light, and a large volume of gas. But because the powder is not contained, it would not produce any significant pressure wave. There would be no explosion, apart from some charring due to the heat of the combustion of the powder, the table would be essentially unharmed, as would any objects which happened to be sitting on the table next to the powder.

Now, at the other end of the spectrum, say that you take two ounces of that same powder and pour it into an oblong iron container shaped like a MkII fragmentation grenade of the sort used by the US Army during all of the major conflicts of the mid 20th century.

If you ignite the powder inside of that container, it will cause the pressure inside of the container to increase rapidly and to a very high level, until the container itself yields. When this occurs, there will be an extremely violent release of pressure into the surrounding environment, creating a blast wave which is capable of inflicting percussive injury in addition to propelling fragments of the container at velocities comparable to that of a bullet and capable of inflicting serious wounds in soft tissue.

Between these two extremes lies a continuum of outcomes, in which the volume of the propellant and the design of the container play a give-or-take battle to produce outcomes which vary from *foof* all the way to *BOOM*.

To my admittedly inexperienced mind, a pressure cooker seems like such a weak vessel that a very large volume of low-order propellant combusting inside of it would produce an outcome which is closer to the 5 lbs of powder on the table, as compared to the much stronger pipe containing a smaller amount of propellant, which would seem to be closer to the MkII grenade.

Quote:

I reckon their safety vents aren't an issue for bomb making purposes because they won't flow fast enough to reduce the explosiveness.

Yeah, the vent is as irrelevant here as trying to bail out the Titanic with a teaspoon. It's the overall structure of the thing which makes no sense to me, including the interface of the lid to the pot.

The "pressure cookers", or the remains of them shown on TV and news outlets seem pretty wimpy. Paper thin, stamped steel. My mom's cooker is cast aluminum, and probably close to 1/4" thick. The lid locks on with interlocking rings, similar to a large caliber artillery breach. The vent/regulator is a tube sticking up the middle of the lid, with a weight that fits over it. It hisses and rattles like a demon.

It also has this 1/2" black rubber plug off to one side. After 40+ years, that rubber plug is as hard as a rock. I'm sure it would explode with quite some force if the main vent/regulator thingy failed.

Consider that you don't always need a pressure vessel to produce a violent explosion...

RDX and PETN come to mind.

RDX and PETN do not need any sort of pressure vessel to be deadly in small quantities.

Quite the contrary; once an explosion is initiated in RDX, the combustion of the remainder of the material happens so quickly that the time to ignite it all is effectively zero - basically combustion occurs at the speed of sound, but because the initial blast has packed the immediately surrounding material so densely, the speed of sound through the now densely packed material approaches what is practically infinity for our purposes, so instead of requiring a pressure vessel to force homogenous propogation of the explosive, it simply requires a strong and capable ignition source - such as a blasting cap. Blasting caps can fit inside of a mcdonalds drink straw, and are about 3.5 inches long. Electric blasting caps are very sensitive, and can possibly be ignited with the voltage required to activate the "ring" speaker on a nokia 6700.

Put 1.25 lbs of RDX, a Blasting Cap, and a pay-as-you-go cell phone into a pressure cooker, and what do you have?.....

....Room for another 5 lbs of RDX...if it's a small pressure cooker.

Lucky for us, it seems that the pressure cooker bomber didn't have access to RDX, or the more potent PETN. A single 1.25 lb. block of RDX (Or the name you're more familiar with: C-4) would have probably caused greater damage measured on an order of magnitudes of the actual blast....without any additional shrapnel involved. I have cut large steel I-Beams with nothing more than a few correctly placed open-air half-pound blocks of RDX.

Location: Chicago (Over two miles from Wrigley Field. Fuck the Cubs. Fuck them in their smarmy goat-hole.)

Posts: 26,317

Total Cats: 1,915

Quote:

Originally Posted by rleete

The "pressure cookers", or the remains of them shown on TV and news outlets seem pretty wimpy. Paper thin, stamped steel.

Yup.

My grandmother used to have a pressure cooker which sounds like the one you describe. It was made from the melted-down remnants of a Soviet tank, and the fastening mechanism of the lid was the inspiration for the design of the breech in the 16"/50 caliber Mark 7 cannon used aboard the Iowa-class battleships.

Quote:

Originally Posted by fooger03

Consider that you don't always need a pressure vessel to produce a violent explosion...

RDX and PETN come to mind.

That was exactly my point in post #68, wherein I posited to myself "Well, what if I'm wrong in that fundamental assumption? If a high-order explosive such as TNT or RDX or even something like ANFO were used, then the container of the device becomes less an active agent in determining its yield than simply a thing to put the explosive agent in and provide an affordance for packing shrapnel around."

In a situation in which the supplies used to make the device are supplied by a state, or by a quasi-military organization with access to basic demolition equipment, such a scenario would be easily rationalized.

But it seems to me that most of the contemporary literature indicates the use of low-order explosives / propellants.

And for that, you need a strong casing in order to transform a simple deflagration into an actual explosion.

Then of course you have the conspiracy theorists saying these 2 guys are Government agents. The guy in the hat with the white symbol is the punisher symbol, which is also the symbol for the late Chris Kyle (former US Navy Seal sniper)

Hat seen here on Chris Kyle himself: (not saying it is CHris in the above photo, you can order these hats)

So I wouldn't say its the end of them trying to pin it on a "Right wing extremist group"